1. Field of the Invention
The invention pertains to a piston-cylinder assembly of the type having a piston rod which is guided axially in a container tube and at least partially covered by a bellows. A resilient stop pad installed concentrically on the piston rod comes to rest on an end cap fitted to the container tube at the end of inward travel of the piston rod.
2. Description of the Related Art
DE 1 965 945 A1 describes a piston-type shock absorber, the piston rod of which is covered by a resilient stop pad combined with a bellows. The resilient stop pad and the bellows form an independent assembly, the bellows being attached to the bottom end of the resilient stop pad. As a result, the end of the resilient stop pad is held coaxially on the adjacent end of the bellows. The end of the bellows facing the cylinder is positioned radially by a sleeve section of the spring collar. No provision is made for holding the end of the bellows in position axially with respect to the sleeve section. On the contrary, it can be assumed that this end of the bellows is free to move in the axial direction within a predetermined scope between the spring collar and one edge of the stop sleeve. At the maximum amount of inward travel, the resilient stop pad is supported on the stop sleeve. The bellows, at this maximum amount of inward travel, does not absorb any of the compressive forces being exerted on any of the components of the piston-type shock absorber.
DE 91 09 202 U1 describes a cylinder tube end cap for a vibration damper. In an exemplary embodiment, a circumferential edge of this cap enters into a form-locking connection with a bellows. The bellows itself is clamped between a disk, against the bottom of which a resilient stop pad is supported, and an elastic support body. During assembly, the cylinder tube end cap is pressed onto the end of the container tube. Then the resilient stop pad is pushed onto the piston rod, and the bellows is snapped onto the disk mentioned above. The cylinder tube end cap and the bellows cannot be made as a prefabricated assembly, because otherwise the disk with the resilient stop pad could no longer be introduced into the bellows.
DE 41 37 447 A1 discloses a telescoping shock absorber, on the piston rod outlet end of which an end cap is attached to the container tube. In addition, the piston-cylinder assembly includes a resilient stop pad, which is supported axially against a spring collar. A bellows is snapped into a sleeve part of a spring collar on the vehicle body side of the assembly. During final assembly of the piston-cylinder assembly, the pretension in the pushing direction pushes the bottom end of the bellows into a form-locking connection with a circumferential edge of the end cap. For this purpose, the bottom end of the bellows must be able to expand in the radial direction. In the case of a vehicle suspension spring with a comparatively small inside diameter, it is possible for the bottom edge of the bellows to come into contact with the suspension spring, which makes it impossible to execute the required installation motion.
It is also necessary for the bellows to be relatively stiff, which can be accomplished by the choice of material out of which it is made or its geometry. This relative stiffness, however, has a negative effect on the fatigue strength of the bellows. The relationship here, however, is that the greater the stiffness, the greater the stress within the material of the bellows during the continual inward and outward travel of the piston-cylinder assembly.